The invention relates to the detection and identification of explosives and other controlled substances.
To protect public safety and prevent terrorist activity it is important to detect hidden explosives. For example, many airports routinely use x-ray scanning systems to identify explosives or other violent weapons hidden within baggage. Also, airports and bomb squads routinely use xe2x80x9csniffingxe2x80x9d detection devices that absorb particulate or vapor matter and analyze the matter for the presence of explosives. Analytical techniques used by such detection devices include ion mobility spectrometry (IMS) and gas chromatography.
Explosives can be made from a wide range of energetic materials including, e.g., organic nitrates, organonitro compounds, ketone and acyl peroxides, inorganic chlorates, perchlorates, nitrates, fulminates, and acetylides. Unfortunately, because of the wide range of energetic materials and the many differences in their physical properties, several detection devices detect only certain types of explosives and fail to detect others. For example, many detection devices readily detect conventional explosives made of organic nitro and nitrate compounds, but fail to detect explosives made of inorganic nitrates or non-nitrogeneous compounds. In particular, many nitrogen-based detection devices fail to detect explosives such as ANFO (ammonium nitrate in fuel oil), Black Powder (xe2x80x9cgun powderxe2x80x9d formed from potassium nitrate, sulfur, and charcoal), and triacetone triperoxide (TATP). As a result, such explosives are sometimes referred to as xe2x80x9ctransparent.xe2x80x9d Moreover, TATP, for example, can be easily prepared in a basement lab using commercially available starting materials obtained from, e.g., hardware stores, pharmacies, and stores selling cosmetics, and can be as or more powerful than military analogs.
In addition to detecting hidden explosives, it is also desirable to identify the particular type of explosive once it is detected to assess its danger, deactivate it, and/or provide forensic evidence.
Detection and identification of other controlled substances such as narcotic drugs is also important. To insure public safety, law enforcement officials try to detect and identify hidden quantities of narcotic drugs. Where possible, law enforcement officials also try to provide proper identification of the detected drugs as forensic evidence.
The invention features methods and systems for detecting the presence of an explosive in a sample of unknown material. The methods and systems are based in part on the recognition that all self-contained explosives decompose and release significant amounts of energy upon thermal excitation, whereas most other materials absorb energy upon thermal decomposition. The released energy can be used to detect small quantities of explosive hidden in a sample of unknown composition. Thus, the presence of an explosive in a unknown sample can be detected by thermally analyzing the unknown sample to produce a thermogram and determining whether the thermogram includes a strong exotherm to indicate the presence of the explosive. In particular embodiments it is preferable that the thermal analysis take place in a substantially anaerobic environment to minimize exothermic reactions with oxygen. Various methods can be used to conduct the thermal analysis including differential thermal analysis (DTA), quantitative differential thermal analysis (QDTA), dynamic differential calorimetry (DDC), dynamic enthalpic analysis (DEA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).
In another aspect, and in addition to detecting the general presence of an explosive in an unknown sample, the new methods and systems can identify the specific type of explosive by comparing the measured thermogram for the unknown sample to reference thermograms for particular types of explosives. Similarly, the presence of a particular drug or any other contraband material in a sample of unknown composition can be detected and identified by comparing the sample thermogram to reference thermograms for particular types of drugs and contraband materials, e.g., cocaine and heroin.
In general, in one aspect, the invention features a method for detecting the presence of an energetic material in a sample in which the presence of the energetic material is unknown. The method includes the steps of: heating the sample; measuring heat flow between the sample and its surrounding environment, e.g., by using differential scanning calorimetry; and analyzing the measured heat flow between the sample and its surrounding environment. An exothermal peak in the measured heat flow indicates the presence of the energetic material in the sample.
The heating step can include heating the sample from about room temperature to a temperature of at least 200xc2x0 C., but, in some embodiments, not greater than about 550xc2x0 C., and in other embodiments, not greater than about 350xc2x0 C. Alternatively, or in addition, the heating step can include heating the sample in a substantially anaerobic environment.
In some embodiments, the sample includes a plurality of particles, which can be collected from air samples, surfaces of passenger clothing, luggage, and cargo. In particular, to prevent terrorist activities, the sample can be collected from an airport environment.
In another aspect, the invention features a system for detecting the presence of an energetic material in a sample in which the presence of the energetic material is unknown. The system includes: a thermal measuring apparatus (e.g., a differential scanning calorimeter) which during operation heats the sample and measures heat flow between the sample and its surrounding environment; and an analyzer coupled (e.g., electrically) to the thermal measuring apparatus which during operation analyzes the heat flow measured by the thermal measuring apparatus to determine the presence or absence of an exothermal peak. The presence of an exothermal peak indicates the presence of the energetic material in the sample and the absence of an exothermal peak indicates the absence of any energetic material in the sample.
The thermal measuring apparatus can be configured to heat the sample from about room temperature to a temperature of at least 200xc2x0 C., but, in some embodiments, not greater than about 550xc2x0 C., and in other embodiments, not greater than about 350xc2x0 C. Alternatively, or in addition, the thermal measuring apparatus can be configured to heat the sample in a substantially anaerobic environment.
The detection system can also include a collection apparatus that collects and concentrates the sample, e.g., by electrostatic precipitation or by solvent extraction with a volatile organic solvent.
In general, in another aspect, the invention features a method for identifying the presence of a contraband material (e.g., an explosive or illegal drug) in a test sample in which the presence of the contraband material is unknown. The identification method includes: heating the test sample; measuring heat flow between the test sample and its surrounding environment to produce a test thermogram, e.g., by using differential scanning calorimetry; and comparing features of the test thermogram to features of reference thermograms for reference samples including known contraband materials. A match of a reference thermogram with the test thermogram identifies the presence of a contraband material. To determine such a match, the temperatures of exotherms, endotherms, or both exotherms and endotherms, in the thermogram of the test sample can be compared with the temperatures of exotherms, and endotherms in the reference thermograms. In some embodiments, the sample is heated in a substantially anaerobic environment.
In yet another aspect, the invention features a system for identifying the presence of a contraband material (e.g., an explosive or an illegal drug) in a test sample in which the presence of the contraband material is unknown. The identification system includes: a thermal measuring apparatus (e.g., a differential scanning calorimeter) which during operation heats the test sample, measures heat flow between the test sample and its surrounding environment, and records a test thermogram of the test sample based on the measured heat flow; and an analyzer coupled to the thermal measuring apparatus which during operation compares features of the test thermogram to features of one or more reference thermograms for reference samples including known contraband materials and determines whether there is a match between a reference thermogram and the test thermogram to identify the presence of a contraband material. The system can further include a collection system that collects and concentrates the sample.
The reference thermogram stored in the analyzer can be that of an explosive or a drug. In addition, the analyzer can store a set of reference thermograms. Also, to determine the match, the analyzer can compare the temperatures of exotherms, endotherms, or exotherms and endotherms in the thermogram of the test sample with temperatures of exotherms and endotherms in the reference thermograms.
Energetic materials are materials that undergo exothermal decomposition in an anaerobic environment. Explosives are a subset of energetic materials in which the exothermal decomposition is rapid and self-sustaining, releasing large amounts of heat and pressure. The exothermal decomposition for energetic materials and explosives can be triggered by heat and/or mechanical shock. An anaerobic environment is an environment in which oxygen is absent. A substantially anaerobic environment can be produced by purging an enclosed chamber with an inert gas, e.g., nitrogen, or continuously flowing the inert gas through an open chamber. Under such conditions, the environment can contain less than about 1 percent of oxygen.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The new methods and systems described herein provide a number of advantages. For example, they can detect the presence of a very broad range of explosives, including explosives such as ANFO, Black Powder, and TATP, which are xe2x80x9ctransparentxe2x80x9d to conventional explosive detection methods. In particular, since the detection is based on the presence of an exotherm in a thermogram, which is a general feature of any energetic material, the methods and systems can, in principle, detect the presence of any explosive in an unknown sample. Furthermore, the methods and systems can employ relatively inexpensive, commercially available instruments, such as differential scanning calorimeters (DSCs). Depending on the desired application, such instruments can be selected for rapid thermal analysis and explosive identification such as would be necessary at passenger and baggage gates at airports. Alternatively, cheaper but less rapid instruments can be used in forensic detection of explosives, drugs, or contraband materials.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.